Prolonged use of ibuprofen could hinder testosterone production by the testicles, research suggests.

The study found long-term use of the over-the-counter painkiller resulted in compensated hypogonadism, a condition prevalent among elderly men and associated with reproductive and physical disorders.

Researchers based their findings on a six-week clinical experiment of 31 male participants, aged between 18 and 35.

Writing in the journal Proceedings of the National Academy of Sciences (PNAS), the study authors said: "Concern has been raised over declining male reproductive health in humans.

"Our study addresses this issue by extending data showing anti-androgen effects of analgesics and suggests that such compounds may be involved in adult male reproductive problems."

Dr Richard Quinton, senior lecturer in endocrinology at Newcastle University, said: "This is a landmark study that elegantly combines clinical and basic research, at both tissue and cellular levels, to show that ibuprofen, a common over-the-counter painkiller, can reversibly hinder testosterone production by testicular cells."

Professor Allan Pacey, professor of andrology at the University of Sheffield, said: "The results suggest that long-term use (several weeks) of ibuprofen can affect the production of the male hormone by the testicles.

"The authors speculate that this could have health implications for such men, given the known links between the disruption of such hormones and cardiovascular disease, diabetes and infertility.

"However, this is currently speculative.

"So, for the time being, I would urge men who need to take ibuprofen to continue to do so.

"However, it is recommended that if men (or women) need to take it for more than three days consecutively then they should first consult their family doctor."

The research was carried out by David Mobjerg Kristensen, from the University of Copenhagen, and other authors.